Alcohol-ignition interlocks, which prevent a drinking driver from starting the vehicle, have been demonstrated to be very effective in reducing the recidivism of individuals convicted of driving under the influence (DUI). That evidence has initiated a strong national trend for states to enact legislation requiring interlocks for all DUI offenders. The effectiveness of such legislation is limited, however, because interlocks are only effective while installed on the offender's vehicle (typically 6 months to 2 years), yet DUI offenders generally continue to be an above-average risk to the public for a much longer-up to 7 years. Programs targeted at extending the effectiveness of interlocks beyond the period they are on the offender's vehicle are needed. There is some evidence that brief educational programs and increasing the intensity of the monitoring of interlock performance can reduce recidivism following the removal of the interlock. This application proposes a study covering 10 years of data on 40,000 DUI offenders in Florida, which has implemented an intervention program for interlock users designed to reduce their recidivism following deinstallaton. That program follows a medical model where the need for intervention is determined objectively by interlock breath-test performance rather than by screening interviews. Furthermore, the intervention is applied in stages by increasing the level of treatment provided as an increasing need is demonstrated. The program implements the three types of intervention-education, monitoring, and treatment-for which there is some evidence that they reduce the recidivism of interlock offenders. Where benefits of the interventions can be identified, cost-benefit estimates will be developed for the sample analyzed and for the expected benefit if applied in other states.